The purification of liquids is often required for various reasons. Processes are available for removing impurities from liquids to separate the same in order to properly dispose of the impurities and utilize the pure liquid. Often this is required because the impurities are toxic and otherwise not suitable for ordinary disposal, but require special treatment and handling. In other situations, the aim is to obtain the pure liquid for subsequent use, irrespective of the manner in which the impurities are disposed of using conventional or non-conventional techniques. In the latter category, the purification of ground water is a prime example where chemical impurities and particulate matter are removed so that a potable form of water is available for use.
The purification of water and other liquids takes many forms, including simply filtering the water to remove particulate matter, treating the water chemically to remove both liquid and particulate impurities, and the processing of water by multi-stage systems that accomplish all of the foregoing, in order to provide a purified form of water. Salt water is routinely processed to remove the salt content and other impurities so as to provide potable water. Waste water from ships, industrial facilities, municipalities and other areas is processed to remove the contaminants so that the resulting water can be reused or disposed of in an environmentally safe manner.
The field of petroleum and gas production is an area where a substantial amount of fresh water is used, and a high percentage of the same is returned in the form of highly contaminated water. Here, millions of gallons of fresh water are injected under high pressure conditions into the well to fracture the ground formation and facilitate the production of petroleum or gas therefrom. The water that is returned to the surface in the well (“production water”) during the production of the hydrocarbon resource is liquid in form, and resembles water only in terms of the liquidity thereof. The highly contaminated production water includes many organic and inorganic impurities, has an irritating chemical smell, and is generally brownish in color. The various contaminants resident in the production water include volatile chemicals employed during the fracturing process, calcium, sodium, chlorides, gasses and many other toxic compounds. The production water is not usuable for any other purpose, and thus must be disposed of in a manner that is closely scrutinized. The production water recovered from a well cannot be reused for the production of gas or oil from another well. The five million gallons of fresh water that are injected into a gas well during the fracturing process yield about seventy percent of the same as production water. A gas well can generate production water for many years after it has been opened. Currently, the production water is disposed of by drilling a deep injection well many feet below the ground surface, in an area free of underground water sources, and pumping the production water therein. Many tanker trucks are required to continuously remove the production water from the well site and transport the same to the disposal well. The heavy truck traffic not only places a burden on the roads, which are often rural roads, but also causes highway traffic congestion and other related problems. It can be appreciated that this process is inefficient, costly and environmentally unsafe.
Routine liquid purification techniques include several major technologies, one of which is carbon filtering. Carbon filters are commonly used by passing a stream of water through a bed of carbon material. While this type of filter functions well for its intended purpose, it is adequate for water that is only mildly impure, and is not well adapted for processing huge amounts of water. The inadequacy of a carbon filter is that such a purification process does not remove metals, bacteria and dissolved minerals. Carbon filters are often used in conjunction with other purification processes.
Ion exchange systems are available for removing impurities from water. This type of system employs an ion exchange unit having a bed of beads that is ionically charged so that it attracts impurity ions of an opposite charge. This type of water processing system functions well for home or office use, but requires frequent recharging of the resin bed. This type of system is well adapted for softening water that is already potable.
Reverse osmosis is another process for removing contaminants from water. The reverse osmosis process utilizes one or a series of permeable membranes through which the water is forced. The membranes are constructed with microscopic holes so that generally only water molecules pass through the membrane and other larger molecules, such as chemical and other impurities, are trapped and cannot pass through. However, the reverse osmosis membranes are generally unable to remove all inorganic and organic contaminants. The pressure of the water is significant in order to force the water through the membranes, and generally a substantial area of the reverse osmosis membrane is required. Because of the nature of the process, substantial large-area membranes are required in order to produce a reasonable amount of purified water. A prefiltering system is required in order to remove the larger molecules and particulate matter so that the reverse osmosis membranes do not become clogged in a short period of time. To that end, the cleaning of the reverse osmosis membranes requires frequent attention, and the system must be either shut down, or the contaminated water routed to an alternate off-line reverse osmosis system. Reverse osmosis systems must be very large if required to process a reasonable amount of water per unit of time. In addition, commercial reverse osmosis systems are costly as they tend to be large and require complex subsystems. An example of a reverse osmosis system is described in U.S. Pat. No. 7,306,735.
Distillation systems are well known for removing many types of contaminants from water. The distillation process involves heating the water to a high temperature and then processing the hot water in an environment to flash the water into steam or otherwise vaporize the same. The steam is then condensed to separate the water from the contaminants. These systems are well adapted for removing a high degree of the contaminants, and with the requisite amount of prefiltering, can process a substantial amount of water before the system requires cleaning or disposal of the contaminants. Various distillation systems include U.S. Pat. No. 4,319,964 for the high volume distillation of liquids; U.S. Pat. No. 4,941,330 for a multi-stage flash evaporator; U.S. Pat. No. 5,207,928 for a method for desalination and fresh water recovery; U.S. Pat. No. 6,635,149 for a water purification system, and U.S. Pat. No. 6,740,205 for processing shipboard wastewater.
Many, if not all of the foregoing water purification systems are adapted for purifying a source of water that is not of the toxic type that is produced during the extraction of gas or petroleum from a well. As noted above, the impurity-laden water that is a byproduct of producing gas or oil from a well includes all of the normal contaminants contained in waste water and ground water sources, and many additional contaminants that must be removed in the purification process. In addition, since the production water is produced with a gradually declining volume during production, it is not economical or cost effective to employ a high capacity processing system that meets the initial production water capacity, but is thereafter underutilized. Full utilization of a water processing system can be achieved if centrally located amongst a number of wells, but then the production water must be transported or piped to the processing facility.
From the foregoing, it can be seen that a need exists for an efficient water purification system that can process the impurity-laden production water and produce a purified water output. A need exists for a system that removes contaminants from the production water, or other water source, and is well adapted for removing the collected contaminants as a sludge, to thereby remove the same from the well site in a safe and economical manner. Another need exists for a modular water purification system of the type that can be co-located at the well site with the source of the production water so that no transportation of the production water is necessary. Yet another need exists for a water purification system that is modularized so that after the quantity of production water has subsided, a portion of the system can be removed and transported to another well site and used in parallel with other like systems.